perl6: Switch, another case (pun intended) for unscoped eval

[stefp]

The following implements an enum a la C. It probably has been done before and better. I welcome pointer, but this is not my point. Here I am obliged to use twice the same pattern match. I can't even use qr// because I would have no way (at least in perl5) to get at the capture. TheDamian may had wanted to save away the captures to restore them but $1, $2... are read-only as far as the end-programmer is concerned. I have not peeked at Damian's code but this Switch seems to me yet another case for the scopeless eval.

I already discussed at unscoped eval, but there will never be enough shameless plugs in perlmonks for Perl6 and parrot.

#! /usr/bin/perl
use strict;
use Switch 'Perl6';
use Carp;

sub enum {
  my @enum = split /,/, $_[0];
  my $i = 0;
  for (@enum ) {
    given ($_) {
      when  m/([A-Z]+\d*)(?:\s*=\s*(\d)+)?/i {  
        m/([A-Z]+\d*)(?:\s*=\s*(\d)+)?/i;       
        no strict;
        $i = $2 if defined $2;
        eval "sub $1() { $i }";
        $i++;
    }
      else    { croak qq(bad enum member syntax: "$_") }
    }
  } 
}

enum "INFIX, PREFIX=4, SUFFIX" ;
print INFIX(), ":", PREFIX(), ":",  SUFFIX(), "\n";

-- stefp -- check out TeXmacs wiki

[Elian]

Switch is implemented with source filters, so it doesn't have the same set of issuee as you're facing. (as it's a compile-time source transform rather than a runtime twiddling of things) You might want to take a look at source filters--they're generally more appropriate for new syntax than runtime options.

Which doesn't mean scopeless evals are bad, of course. :)

[stefp]

Certainly enums should be programmed as a filter since stacking filters is allowed.

After filtering by Switch, my program becomes what is listed below and the subroutine Switch::case is called with my regexp as parameter. So, my bad, this seems to be a case for unscoped sub instead of unscoped eval. BTW: I am peeking at parrot and is positively impressed.

use Carp;

sub enum {
  my  @enum = split /,/,  $_[0];
  my  $i = 0;
  for ( @enum ) {
    S_W_I_T_C_H: while (1)  { local $::_S_W_I_T_C_H; Switch::switch  (
+$_);
      if (Switch::case  qr/([A-Z]+\d*)(?:\s*=\s*(\d)+)?/i){ while (1) 
+{  
        m/([A-Z]+\d*)(?:\s*=\s*(\d)+)?/i;       
        no strict;
        $i = $2 if defined $2;
        eval "sub $1() { $i }";
        $i++;
    ;last S_W_I_T_C_H } continue { goto C_A_S_E_1 } last S_W_I_T_C_H; 
+C_A_S_E_1: }
      else    { croak qq(bad enum member syntax: "$_") }
    }continue {last}
  } 
}


enum "INFIX, PREFIX=4, SUFFIX" ;

print INFIX(), ":", PREFIX(), ":",  SUFFIX(), "\n";

-- stefp -- check out TeXmacs wiki

[Anonymous Monk]

FYI: since you welcome a pointer. enum